When I went through my CPLH training in the US it was common practice to go up to 5000 ft + and intentionally bring the aircraft into VRS up to the state where you could watch the sinkrate increase dramatically when slightly adding collective and only little effectiveness on pedals and cyclic left. I never really felt comfortable practicing that manoeuvre as unlike to e.g. a simulated engine failure it just didn‘t feel like having control over the aircraft.
Returning to Europe and converting my FAA license into a European one we only practiced VRS up to the entry stage (vibrations and shaky controls) followed by immediate recovery until positive rate of climb.
When I told the instructor about what we did in the US he looked at me and said:“Well, I guess you‘re lucky you are still here“ followed by a story about bended pitch links as a result of extensive VRS training.
Reading the AH Safety Information Notice
the resulting stresses were not accounted for in component service lives
the following question arises. What exactl would cause those resulting stresses?